A technique for controlling the position and posture of a robot based on information about images captured by the robot with a camera is called visual feedback. When images are captured by a camera mounted on a hand or in the neighborhood of the hand of the robot, an object can be seen in a larger field of view than in a case where the object is captured in an overhead view. Accordingly, the position and posture can be accurately controlled within the image resolution range.
A method of incorporating changes in the image feature amounts of an object into the feedback loop of the robot is called a feature-based method, and according to the method, it is necessary to determine an image Jacobian representing the ratios between changes in image feature amounts and changes in the joint shaft angles of the robot. However, the frame rate of a general-purpose camera is approximately 30 to 60 fps, which is much lower than the control cycles of the robot. Therefore, image feature amounts need to be temporally interpolated to be synchronized with the robot control cycles, and image feature amounts that take into account the movement of the robot in an image need to be estimated.
Depending on the hardware constraints of a robot, the robot cannot move along a target trajectory in some cases. This happens due to a rapid change in the joint shaft angle velocity when a target value is set at or in the neighborhood of a singular point at which there exist an infinite number of solutions to satisfy the joint movement range and the target position and posture of the robot. When a robot cannot be controlled as above, the region is stored as the robot movement inhibiting region, according to a known method of solving the problem.
However, it is not yet known how to calculate a new target value while avoiding such a movement inhibiting region. When a target value is set in the neighborhood of a singular point, the target value can be passed through by sufficiently lowering the velocity on the target trajectory. Therefore, the calculation of the target trajectory in an image is critical.